Not applicable
Not applicable
This invention relates to multimedia teleconferencing systems and methods, and in particular, to high-speed graphics data compression and decompression techniques for use with such systems and methods.
It is time-consuming, difficult, and expensive to set up a combined audio and visual presentation conference between remotely located conference sites. One known approach is video conferencing, which involves two or more video conference devices of the type sold by PictureTel Corporation of Andover, Mass., USA. Such devices are expensive and optimized to support full-motion person-to-person video. They often employ ISDN lines for high-speed data communication, which adds to the total solution cost and hinders mobility of the system. In many instances, full-motion video is unnecessary for an effective conference.
Transmitting computer graphic (CG) data is a different class of problem, relatively unrelated to video conferencing. However, the telephonic transmission of even simple graphics images is unduly time consuming. A common practice among presenters is to display computer-generated visual aids or images. Video conferencing systems typically do not provide convenient tabletop connectivity for integrating presentation images with the video transmission. Rather, it may be necessary to adjust the video conferencing system so that its video camera is aimed toward a screen where presentation images are displayed, e.g., via a computer display or multimedia projector. However, in practice there is insufficient resolution in a video conferencing system, resulting in a low-quality, blurry image that is generally unreadable for normal text.
It is also known to use both a telephone and a computer for sharing presentation materials between a local site and a remote site over a computer network concurrently with an audio telephone conference. In known methods, separate connections are established manually for the voice call (via the telephone network) and for the data or images (via the computer network).
Other data conferencing systems use a centralized computer server to set up and manage the audio and data connections. For example, U.S. Pat. No. 5,916,302 of Dunn et al. describes using a Public Switched Telephone Network (xe2x80x9cPSTNxe2x80x9d) for the audio component of a data conference and a centralized server computer accessible via a computer network for distributing the video or image component of the data conference. Participants using the Dunn et al. system access the server computer to download images using Web browser software of a personal computer.
U.S. Pat. No. 6,233,605 of Watson describes a low-bandwidth remote conferencing system that uses a PSTN for the audio component and networked computers for the visual component. Before a conference, data representing visual images is distributed to computers of conference participants. During the conference, one participant, a leader, periodically issues selection signals to all computers, causing them all to select one of the distributed images and display it. The selection signals and the telephone conference are carried by a single voice-grade telephone channel. The system requires distribution of the presentation images in advance of the telephone conference and does not address the desire to avoid manual interaction with the computer at each site to initiate downloading of the image data. Furthermore, there are some types of presentations for which images cannot be prepared in advance of the presentation and that involve interactive use and display of a software application such as a spreadsheet or drawing program. For example, budget planning and review sessions, design conferences, and distance learning could all benefit from the ability to interact with a software program at one or more of the sites, and have the software program display its output all of the participating sites nearly simultaneously.
While many conference facilities include a network connection point, such as a wall jack for an Ethernet, most facilities do not keep a computer connected to the network. Consequently, a significant amount of time is required to configure the network connection for the computer that will be used at each of the conference sites. The time and difficulty of connecting to the network may be compounded by the use of laptop or other mobile computers that are configured for use with other networks or at other locations within the same network, and not configured for use at the conference site. None of the systems described above overcome the difficulties associated with configuring a computer for connection to a computer network at each of the conference sites in advance of each data conference session.
Wireless interconnectivity techniques have been considered for easing the time and complexity burden associated with setting up multimedia data conferencing systems. However, whether wired or wireless, interconnect systems transfer image data more slowly than desired. Such systems must, therefore, include some sort of data compression and decompression process for transferring images data among components of the system without degrading the image quality. For a system to be suitably xe2x80x9cinteractive, xe2x80x9d the compression and decompression process should transfer a full 1,024 by 768 pixel (xe2x80x9cXGAxe2x80x9d) image between devices, such as a laptop computer and a video projector, in one second or less.
A need exists, therefore, for a highly interactive data conferencing apparatus that includes a wireless high-speed interconnectivity solution and a data conferencing control mechanism.
An object of this invention is, therefore, to provide a data compression and decompression apparatus and a method for wirelessly transferring high-resolution, color image data among devices in one second or less.
Another object of this invention is to provide such an apparatus and method that is perceptively lossless and, therefore, maintains image quality.
A further object of this invention is to provide such an apparatus and method that minimizes the amount of computing resource.
In a data conferencing system suitable for use with this invention, each of two or more geographically separate conference sites has a telephone receiver and a data conferencing appliance coupled to a voice call network, such as a PSTN or PBX. Each site also has a display device, such as a computer display screen or an electronic projector, for displaying images comprised of image data produced by an image source. To facilitate sharing of image data between the sites, a network interface at each site couples a data conference control unit of the data conferencing appliance to a data network that links the sites independently of the voice call network.
In a preferred embodiment, the data conference control unit, telephone receiver, and network interface are integrated in a data conferencing speakerphone appliance that can be conveniently positioned on a conference table at each of the sites and wirelessly coupled to the data network to facilitate data conferencing in accordance with this invention.
In other embodiments, the data conferencing appliance is implemented in software operating on a computer workstation that can also serve as the display device, telephone receiver, and/or image source; or in hardware as a simplified data conferencing appliance that can be used with a separate telephone receiver, display device, and image source. Data conferencing appliances in accordance with the invention may include wireless network connections and automatic network configuration routines for wireless connection of an image source, such as a presenter""s laptop computer, to the data network. Data transfer speed among the wireless connections is enhanced by data compression and decompression processes of this invention.
In particular, the data compression and decompression processes of this invention employ dual compression for first compressing data, such as a computer screen image, and transferring the compressed data over a wireless link, such as an IEEE 802.11b transport medium. The transported compressed image data is then decompressed using dual decompression for reconstructing the original image. The combined compression and decompression technique provides high performance, high image quality, good compression, and is perceptibly lossless. The compression and decompression technique may be used over virtually any wired or wireless communications channel.
In a preferred data compression process of this invention, the data source is a full screen, color, XGA image, which is processed to obtain a bitmap. A two step compression process is employed to obtain the required amount of data compression. The first step employs a color conversion compression process, and the second step employs an Lempel-Ziv-Oberhumer (xe2x80x9cLZOxe2x80x9d) compression process, which generates the compressed data for transmission through a transmission medium.
In a preferred data decompression process of this invention, the compressed data from the LZO compression process is applied to a two step decompression process. The first step employs an LZO decompression process, and the second step employs a color conversion decompression process, which generates decompressed data for rendering a bitmap that is substantially the same as the original bitmap.
High-performance color conversion is required to meet the one second latency goal. Color conversion is normally accomplished with floating point calculations. However there are typically insufficient computing resources available, so a high-speed integer embodiment of this invention is preferably employed. RGB-to-YCrCb co-sited 4:2:0 color conversion is employed to compress the image data. In a preferred embodiment, input RGB data is in a 4:4:4 format, and output YCrCb data is generated in a 4:2:0 format. Of course, other formats may be employed. High performance is achieved by employing factored integer arithmetic. A YCrCb-to-RGB decompression process is employed to reconstitute the compressed image.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof that proceed with reference to the accompanying drawings.